This invention is concerned with novel compounds and other related compounds of general structural formula: ##STR1## and a method of delaying the onset of egg production in young pullets and interrupting the egg production in mature laying hens by administration of one or more of these compounds usually in a feed mix.
Delaying the onset of egg production in the broiler-breeder industry and interrupting the egg production cycle in mature hens in the table egg industry are widely practiced by commercial poultry and egg producers.
The onset of production in young pullets is delayed in essentially all commercial broiler-breeder hens to reduce the number of small eggs produced. Egg size is highly correlated with the age of the bird and chick size is highly correlated with egg size. Therefore, by holding replacement pullets out of production for 2 or 3 weeks at the start of the laying cycle, a larger chicken is produced. It has been shown that layers have a genetic potential for producing a certain number of eggs. Therefore, delaying the onset of egg production does not reduce the total number of eggs laid during a production cycle but does increase the number of large eggs produced.
Interrupting the egg production cycle in commercial layers to improve egg shell and interior egg quality and to extend the production span and life of the hen has been a practice in commercial egg production for several decades. The current methods of interrupting egg production (forced molt) are centered around a stress system of withdrawing feed and/or water for varying time intervals depending on the system used. This stress causes the birds to halt egg production, however, it also causes the birds to go into a full molt (lose feathers). The second physiological effect is believed to be unnecessary and therefore a very undesirable side effect. Once the birds are out of production, a nutritional management regime of restricting feed, water or nutrients is put into effect. The most common procedure is to restrict nutrients by substituting a cereal grain for the laying mash which necessitates two dietary changes during the laying pause. All of the procedures currently practiced require very strict management control which utilizes a large amount of labor and is difficult inasmuch as an overly restrictive program will result in an abnormally high incidence of mortality in the layer flock, while a lenient program will result in an undesirably slow cessation in egg production. Also, switching the hens to a grain diet, low in nutrients, does not afford the hen an opportunity to regenerate her body nutrient stores. Regeneration does not take place until the hen is again placed on the high nutrient diet. Within a few days after receiving the adequate diet, the hen resumes egg production and there is inadequate time for her to rebuild body stores.
Surprisingly it has been found that compounds of a class known generically as 2-(substituted phenylimino)imidazolidines, some of which are novel, are anovulatory agents which on administration to young pullets delay the onset of egg production with the benefits inherent therein, and on administration to laying hens cause a reversible interruption in egg production with all the beneficial effects of a traditional forced molt procedure. The novel method described herein has the added advantages of: a reduction in bird mortality; a more uniform cessation of egg production; a more uniform return to full egg production; maintenance of the birds on a nutritionally adequate diet during the production pause; reduction in labor and management costs; and greater flexibility in the timing of the laying interruption.
It is therefore an object of this invention to provide a group of 2-(substituted phenylimino)imidazolidines which are anovulatory agents some of which are novel.
It is also an object of this invention to provide a novel method of mimicking a forced molt in laying hens with all of the advantages and none of the disadvantages inherent therein which comprises the administration of an anovulatory 2-(substituted phenylimino)imidazolidine.
It is a further object of this invention to provide novel compositions for administration of the anovulatory 2-(substituted phenylimino)imidazolidines to laying hens.
Other objects are inherent in the foregoing or will become apparent from the following.